Collapse: Identification of factors regulating arbuscule degeneration

• Applicant: Dr. Riikka Mäkilä
• Subject Area: Plant Genetics and Genomics ; Organismic Interactions, Chemical Ecology and Microbiomes of Plant Systems
• Term: since 2026
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 576489902

Arbuscular mycorrhiza (AM) is an ancient symbiosis between the majority of land plants and fungi of the Glomeromycotina. This mutualistic association provides plants with water and minerals in exchange for sugars and lipids, improving their yield and fitness and making AM a potential addition to sustainable agricultural practices. At the centre of the symbiosis are branched tree-shaped fungal structures, called arbuscules, that develop in inner cortex cells of the root. A plant-derived periarbuscular membrane separates arbuscules from the plant cell cytoplasm and forms the main interface for nutrient exchange between the symbionts. Arbuscule development is highly dynamic and regulated by the plant in accordance with its physiological state. Lifetime of an arbuscule in a cell is between 2 and 5 days, after which they collapse and are cleared from the cell. The same cell may be later recolonised. The transient nature of the arbuscules is speculated to serve for example as a mechanism to defer fungal parasitism or to eliminate inefficient structures. Although multiple regulators influencing arbuscule formation and function have been identified, very little is known about the factors regulating their collapse. The transcription factor MYB1 was shown to be involved in this process by inducing the expression of genes encoding hydrolytic enzymes. This research project aims to unravel the mechanisms regulating arbuscule collapse using MYB1 as a starting point. I will explore the function and regulation of MYB1 by identifying its downstream targets and interacting proteins. In addition, I will generate a stage-specific visual marker for collapsing arbuscules to enable an increased phenotypic resolution. To better understand the role of MYB1 in arbuscule collapse, I want to identify its direct targets and downstream genes. To find downstream genes I will use RNAseq analysis of the mutant and overexpression lines and for identifying direct targets bound by MYB1 I will use CUT&Tag. Transcription factors often work in larger protein complexes to regulate gene expression. I plan to use proximity labelling to identify the proteins interacting with MYB1. The characterisation of these proteins will help us to understand how the arbuscule collapse is regulated. Thus, I wish to fill a major knowledge gap on the dynamic developmental regulation of central structures within one of the most widespread symbioses on Earth.

• DFG Programme: Position